Thin layers of grafted polymer chains were produced by ultraviolet light-induced graft polymerization of a hydrophilic monomer, methacryloxyethyl phosphate, onto the Ar plasma-pretreated film surface of high-density polyethylene. The hydrogen-bonding interactions in the grafted polymer and the wettability of the grafted layers were studied by Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy and water contact angle measurements, respectively The grafted layers exhibited a distinct wetting transition with an increase in the graft, density, which closely correlated with a clearly observable change in the hydrogen-bonding extent of the grafted chains.